Compact and Low-Volume Mechanical Igniter and Ignition Systems For Thermal Batteries and the Like

ABSTRACT

An inertial igniter including: a body having a base and three or more posts, each post having a hole; a locking ball corresponding to each post, wherein a portion of the locking balls are disposed in the hole; a striker mass movably disposed relative to the posts and having a surface corresponding to the posts, the striker mass further having a concave portion corresponding to the locking balls, wherein a second portion of each locking ball is disposed in a corresponding concave portion for retaining the striker mass relative to the posts; a collar movable relative to the posts; and a biasing element for biasing the collar in a first position which retains the striker mass, the biasing element permitting movement of the collar to a second position to release the striker mass relative to the posts upon a predetermined acceleration profile.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the benefit of U.S. Provisional Application No.61/239,048 filed on Sep. 1, 2009, the entire contents of which isincorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to mechanical igniters, and moreparticularly to compact, low-volume, reliable and easy to manufacturemechanical igniters and ignition systems for thermal batteries and thelike.

2. Prior Art

Thermal batteries represent a class of reserve batteries that operate athigh temperature. Unlike liquid reserve batteries, in thermal batteriesthe electrolyte is already in the cells and therefore does not require adistribution mechanism such as spinning. The electrolyte is dry, solidand non-conductive, thereby leaving the battery in a non-operational andinert condition. These batteries incorporate pyrotechnic heat sources tomelt the electrolyte just prior to use in order to make themelectrically conductive and thereby making the battery active. The mostcommon internal pyrotechnic is a blend of Fe and KClO₄. Thermalbatteries utilize a molten salt to serve as the electrolyte uponactivation. The electrolytes are usually mixtures of alkali-halide saltsand are used with the Li(Si)/FeS₂ or Li(Si)/CoS₂ couples. Some batteriesalso employ anodes of Li(Al) in place of the Li(Si) anodes. Insulationand internal heat sinks are used to maintain the electrolyte in itsmolten and conductive condition during the time of use. Reservebatteries are inactive and inert when manufactured and become active andbegin to produce power only when they are activated.

Thermal batteries have long been used in munitions and other similarapplications to provide a relatively large amount of power during arelatively short period of time, mainly during the munitions flight.Thermal batteries have high power density and can provide a large amountof power as long as the electrolyte of the thermal battery stays liquid,thereby conductive. The process of manufacturing thermal batteries ishighly labor intensive and requires relatively expensive facilities.Fabrication usually involves costly batch processes, including pressingelectrodes and electrolytes into rigid wafers, and assembling batteriesby hand. The batteries are encased in a hermetically-sealed metalcontainer that is usually cylindrical in shape. Thermal batteries,however, have the advantage of very long shelf life of up to 20 yearsthat is required for munitions applications.

Thermal batteries generally use some type of igniter to provide acontrolled pyrotechnic reaction to produce output gas, flame or hotparticles to ignite the heating elements of the thermal battery. Thereare currently two distinct classes of igniters that are available foruse in thermal batteries. The first class of igniter operates based onelectrical energy. Such electrical igniters, however, require electricalenergy, thereby requiring an onboard battery or other power sources withrelated shelf life and/or complexity and volume requirements to operateand initiate the thermal battery. The second class of igniters, commonlycalled “inertial igniters”, operates based on the firing acceleration.The inertial igniters do not require onboard batteries for theiroperation and are thereby often used in high-G munitions applicationssuch as in gun-fired munitions and mortars.

In general, the inertial igniters, particularly those that are designedto operate at relatively low impact levels, have to be provided with themeans for distinguishing events such as accidental drops or explosionsin their vicinity from the firing acceleration levels above which theyare designed to be activated. This means that safety in terms ofprevention of accidental ignition is one of the main concerns ininertial igniters.

In recent years, new improved chemistries and manufacturing processeshave been developed that promise the development of lower cost andhigher performance thermal batteries that could be produced in variousshapes and sizes, including their small and miniaturized versions.However, the existing inertial igniters are relatively large and notsuitable for small and low power thermal batteries, particularly thosethat are being developed for use in miniaturized fuzing, future smartmunitions, and other similar applications.

The need to differentiate accidental and initiation accelerations by theresulting impulse level of the event necessitates the employment of asafety system which is capable of allowing initiation of the igniteronly during high total impulse levels. The safety mechanism can bethought of as a mechanical delay mechanism, after which a separateinitiation system is actuated or released to provide ignition of thepyrotechnics. An inertial igniter that combines such a safety systemwith an impact based initiation system and its alternative embodimentsare described herein together with alternative methods of initiationpyrotechnics.

Inertia-based igniters must therefore comprise two components so thattogether they provide the aforementioned mechanical safety (delaymechanism) and to provide the required striking action to achieveignition of the pyrotechnic elements. The function of the safety systemis to fix the striker in position until a specified acceleration timeprofile actuates the safety system and releases the striker, allowing itto accelerate toward its target under the influence of the remainingportion of the specified acceleration time profile. The ignition itselfmay take place as a result of striker impact, or simply contact orproximity. For example, the striker may be akin to a firing pin and thetarget akin to a standard percussion cap primer. Alternately, thestriker-target pair may bring together one or more chemical compoundswhose combination with or without impact will set off a reactionresulting in the desired ignition.

In addition to having a required acceleration time profile which willactuate the device, requirements also commonly exist for non-actuationand survivability. For example, the design requirements for actuationfor one application are summarized as:

1. The device must fire when given a [square] pulse acceleration of 900G±150 G for 15 ms in the setback direction.

2. The device must not fire when given a [square] pulse acceleration of2000 G for 0.5 ms in any direction.

3. The device must not actuate when given a ½-sine pulse acceleration of490 G (peak) with a maximum duration of 4 ms.

4. The device must be able to survive an acceleration of 16,000 G, andpreferably be able to survive an acceleration of 50,000 G.

A schematic of a cross-section of a conventional thermal battery andinertial igniter assembly is shown in FIG. 1. In thermal batteryapplications, the inertial igniter 10 (as assembled in a housing) isgenerally positioned above the thermal battery housing 11 as shown inFIG. 1. Upon ignition, the igniter initiates the thermal batterypyrotechnics positioned inside the thermal battery through a providedaccess 12. The total volume that the thermal battery assembly 16occupies within munitions is determined by the diameter 17 of thethermal battery housing 11 (assuming it is cylindrical) and the totalheight 15 of the thermal battery assembly 16. The height 14 of thethermal battery for a given battery diameter 17 is generally determinedby the amount of energy that it has to produce over the required periodof time. For a given thermal battery height 14, the height 13 of theinertial igniter 10 would therefore determine the total height 15 of thethermal battery assembly 16. To reduce the total volume that the thermalbattery assembly 16 occupies within a munitions housing, it is thereforeimportant to reduce the height of the inertial igniter 10. This isparticularly important for small thermal batteries since in such casesthe inertial igniter height with currently available inertial igniterscan be almost the same order of magnitude as the thermal battery height.

With currently available inertial igniters, a schematic of which isshown in FIG. 2, the inertial igniter 20 may have to be positionedwithin a housing 21 as shown in FIG. 3, particularly for relativelysmall igniters. The housing 21 and the thermal battery housing 11 mayshare a common cap 22, with the opening 25 to allow the ignition fire toreach the pyrotechnic material 24 within the thermal battery housing. Asthe inertial igniter is initiated, the sparks can ignite intermediatematerials 23, which can be in the form of thin sheets to allow for easyignition, which would in turn ignite the pyrotechnic materials 24 withinthe thermal battery through the access hole 25.

A schematic of a cross-section of a currently available inertial igniter20 is shown in FIG. 2 in which the acceleration is in the upwarddirection (i.e., towards the top of the paper). The igniter has sideholes 26 to allow the ignition fire to reach the intermediate materials23 as shown in FIG. 3, which necessitate the need for its packaging in aseparate housing, such as in the housing 21. The currently availableinertial igniter 20 is constructed with an igniter body 60. Attached tothe base 61 of the housing 60 is a cup 62, which contains one part of atwo-part pyrotechnic compound 63 (e.g., potassium chlorate). The housing60 is provided with the side holes 26 to allow the ignition fire toreach the intermediate materials 23 as shown in FIG. 3. A cylindricalshaped part 64, which is free to translate along the length of thehousing 60, is positioned inside the housing 60 and is biased to stay inthe top portion of the housing as shown in FIG. 2 by the compressivelypreloaded helical spring 65 (shown schematically as a heavy line). Aturned part 71 is firmly attached to the lower portion of thecylindrical part 64. The tip 72 of the turned part 71 is provided withcut rings 72 a, over which is covered with the second part of thetwo-part pyrotechnic compound 73 (e.g., red phosphorous).

A safety component 66, which is biased to stay in its upper mostposition as shown in FIG. 2 by the safety spring 67 (shown schematicallyas a heavy line), is positioned inside the cylinder 64, and is free tomove up and down (axially) in the cylinder 64. As can be observed inFIG. 2, the cylindrical part 64 is locked to the housing 60 by setbacklocking balls 68. The setback locking balls 68 lock the cylindrical part64 to the housing 60 through holes 69 a provided on the cylindrical part64 and the housing 60 and corresponding holes 69 b on the housing 60. Inthe illustrated configuration, the safety component 66 is pressing thelocking balls 68 against the cylindrical part 64 via the preloadedsafety spring 67, and the flat portion 70 of the safety component 66prevents the locking balls 68 from moving away from their aforementionedlocking position. The flat portion 70 of the safety component 66 allowsa certain amount of downward movement of the safety component 66 withoutreleasing the locking balls 68 and thereby allowing downward movement ofthe cylindrical part 64. For relatively low axial acceleration levels orhigher acceleration levels that last a very short amount of time,corresponding to accidental drops and other similar situations thatcause safety concerns, the safety component 66 travels up and downwithout releasing the cylindrical part 64. However, once the firingacceleration profiles are experienced, the safety component 66 travelsdownward enough to release balls 68 from the holes 69 b and therebyrelease the cylindrical part 64. Upon the release of the safetycomponent 66 and appropriate level of acceleration for the cylindricalpart 64 and all other components that ride with it to overcome theresisting force of the spring 65 and attain enough momentum, then itwill cause impact between the two components 63 and 73 of the two-partpyrotechnic compound with enough strength to cause ignition of thepyrotechnic compound.

The aforementioned currently available inertial igniters have a numberof shortcomings for use in thermal batteries, specifically, they are notuseful for relatively small thermal batteries for munitions with the aimof occupying relatively small volumes, i.e., to achieve relatively smallheight total igniter compartment height 13, FIG. 1. Firstly, thecurrently available inertial igniters, such as that shown in FIG. 2, arerelatively long thereby resulting in relatively long total igniterheights 13. Secondly, since the currently available igniters are notsealed and exhaust the ignition fire out from the sides, they have to bepackaged in a housing 21, usually with other ignition material 23,thereby increasing the height 13 over the length of the igniter 20 (seeFIG. 3). In addition, since the pyrotechnic materials of the currentlyavailable igniters 20 are not sealed inside the igniter, they are proneto damage by the elements and cannot usually be stored for long periodsof time before assembly into the thermal batteries unless they arestored in a controlled environment.

SUMMARY OF THE INVENTION

A need therefore exists for novel miniature inertial igniters forthermal batteries used in gun fired munitions, particularly for smalland low power thermal batteries that could be used in fuzing and othersimilar applications, thereby eliminating the need for external powersources. The innovative inertial igniters can be scalable to thermalbatteries of various sizes, in particular to miniaturized igniters forsmall size thermal batteries. Such inertial igniters must be safe and ingeneral and in particular they should not initiate if dropped, e.g.,from up to 7 feet onto a concrete floor for certain applications; shouldwithstand high firing accelerations, for example up to 20-50,000 Gs; andshould be able to be designed to ignite at specified acceleration levelswhen subjected to such accelerations for a specified amount of time tomatch the firing acceleration experienced in a gun barrel as compared tohigh G accelerations experienced during accidental falls which last oververy short periods of time, for example accelerations of the order of1000 Gs when applied for 5 msec as experienced in a gun as compared tofor example 2000 G acceleration levels experienced during accidentalfall over a concrete floor but which may last only 0.5 msec. Reliabilityis also of much concern since the rounds should have a shelf life of upto 20 years and could generally be stored at temperatures of sometimesin the range of −65 to 165 degrees F. This requirement is usuallysatisfied best if the igniter pyrotechnic is in a sealed compartment.The inertial igniters must also consider the manufacturing costs andsimplicity in design to make them cost effective for munitionsapplications.

To ensure safety and reliability, inertial igniters should not initiateduring acceleration events which may occur during manufacture, assembly,handling, transport, accidental drops, etc. Additionally, once under theinfluence of an acceleration profile particular to the firing ofordinance from a gun, the device should initiate with high reliability.In many applications, these two requirements often compete with respectto acceleration magnitude, but differ greatly in impulse. For example,an accidental drop may well cause very high acceleration levels—even insome cases higher than the firing of a shell from a gun. However, theduration of this accidental acceleration will be short, therebysubjecting the inertial igniter to significantly lower resulting impulselevels. It is also conceivable that the igniter will experienceincidental low but long-duration accelerations, whether accidental or aspart of normal handling, which must be guarded against initiation.Again, the impulse given to the miniature inertial igniter will have agreat disparity with that given by the initiation acceleration profilebecause the magnitude of the incidental long-duration acceleration willbe quite low.

Those skilled in the art will appreciate that the inertial ignitersdisclosed herein may provide one or more of the following advantagesover prior art inertial igniters:

provide inertial igniters that are significantly shorter and smaller involume than currently available inertial igniters for thermal batteriesor the like, particularly relatively small thermal batteries to be usedin munitions without occupying very large volumes;

provide inertial igniters that can be mounted directly onto the thermalbatteries without a housing (such as housing 21 shown in FIG. 3),thereby allowing even a smaller total height and volume for the inertialigniter assembly;

provide inertial igniters that can directly initiate the pyrotechnicsmaterials inside the thermal battery without the need for intermediateignition material (such as the additional material 23 shown in FIG. 3)or a booster;

provide inertia igniters that could be constructed to guide thepyrotechnic flame essentially downward (in the direction opposite to thedirection of the firing acceleration—usually for mounting on the top ofthe thermal battery as shown in FIG. 3), or essentially upward (in thedirection opposite of the firing acceleration—usually for mounting atthe bottom of the thermal battery), or essentially sidewise (lateral tothe direction of the firing);

provide inertial igniters that allow the use of standard off-the-shelfpercussion cap primers instead of specially designed pyrotechniccomponents; and

provide inertial igniters that can be sealed to simplify storage andincrease their shelf life.

Accordingly, inertial igniters and ignition systems for use with thermalbatteries for producing power upon acceleration are provided.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features, aspects, and advantages of the apparatus ofthe present invention will become better understood with regard to thefollowing description, appended claims, and accompanying drawings where:

FIG. 1 illustrates a schematic of a cross-section of a thermal batteryand inertial igniter assembly.

FIG. 2 illustrates a schematic of a cross-section of a conventionalinertial igniter assembly known in the art.

FIG. 3 illustrates a schematic of a cross-section of a conventionalinertial igniter assembly known in the art positioned within a housingand having intermediate materials for ignition.

FIG. 4 illustrates a schematic of a cross-section of a first embodimentof an inertial igniter in a locked position.

FIG. 5 a illustrates a schematic of the isometric drawing of a firstembodiment of an inertial igniter together with the top cap of a thermalbattery to which it is attached.

FIG. 5 b illustrates a second view of the isometric drawing of the firstembodiment of the inertial igniter of FIG. 5 a showing the openings thatare provided to exit the ignition sparks and flames into the thermalbattery.

FIG. 5 c illustrates a schematic of the isometric drawing of a firstembodiment of an inertial igniter of FIG. 5 a without the outer housing(side wall and top cap) of the inertial igniter.

FIG. 6 illustrates the inertial igniter of FIG. 4 upon a non-firingaccidental acceleration.

FIG. 7 illustrates the inertial igniter of FIG. 4 upon a firingacceleration.

FIG. 8 illustrates the inertial igniter of FIG. 4 upon the striker massimpacting base, causing the initiation of ignition of the two-partpyrotechnic compound.

FIG. 9 illustrates a schematic of a cross-section of a second embodimentof an inertial igniter in a locked position.

FIG. 10 illustrates a schematic of a cross-section of a third embodimentof an inertial igniter in initiation position.

FIGS. 11 a and 11 b illustrate an isometric and a schematic of across-section, respectively, of a fourth embodiment of an inertialigniter in initiation position.

FIG. 12 illustrates a schematic of a cross-section of a fifth embodimentof an inertial igniter in a locked position.

FIG. 13 illustrates an isometric cut away view of a sixth embodiment ofan inertial igniter.

FIG. 14 illustrates a full isometric view of the inertial igniter ofFIG. 13.

FIGS. 15 a and 15 b illustrate first and second variations of thermalbattery and inertial igniter assemblies.

FIG. 16 illustrates a first variation of the inertial igniter of FIG.13.

FIG. 17 illustrates a second variation of the inertial igniter of FIG.13.

FIG. 18 illustrates a third variation of the inertial igniter of FIG.13.

FIG. 19 illustrates a thermal battery/inertial igniter assembly in whichmore than one inertial igniter is used.

FIG. 20 a illustrates a top view and FIG. 20 b illustrates an isometricview of a bottom plate and posts for a gang of three inertial igniters.

FIG. 21 a illustrates a top view and FIG. 21 b illustrates an isometricview of a bottom plate and posts for a variation of the gang of threeinertial igniters of FIGS. 20 a and 20 b.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

A schematic of a cross-section of a first embodiment of an inertiaigniter is shown in FIG. 4, referred to generally with reference numeral30. The inertial igniter 30 is constructed with igniter body 31,consisting of a base 32 and at least two posts 33, and a housing wall34. The base 32 and two posts 33, which may be integral or may have beenconstructed as separate pieces and joined together, for example bywelding of press fitting or other methods commonly used in the art. Inthe schematic of FIG. 4, the igniter body 31 and the housing wall 34 areshown to be joined together at the base 32; however, the two componentsmay be integrated as one piece and a separate top cap 35 may then beprovided, which is then joined to the top surface of the housing 34following assembly of the igniter (in the schematic of FIG. 4 the topcap 35 is shown as an integral part of the housing 34). In addition, thebase of the housing 32 may be extended to form the cap 36 of the thermalbattery 37, the top portion of which is shown with dashed lines in FIG.4.

The inertial igniter 30 with the thermal battery top cap 36 is shown inthe isometric drawings of FIGS. 5 a and 5 b. The inertial igniterwithout its housing 34 and top cap 35 is shown in the isometric drawingof FIG. 5 c. The base of the housing 32 is also provided with at leastone opening 38 (with corresponding openings in the thermal battery topcap 36) to allow the ignited sparks and fire to exit the inertialigniter into the thermal battery 37 upon initiation of the inertialigniter pyrotechnics 46 and 47, FIG. 4, or percussion cap primer whenused in place of the pyrotechnics 46 and 47 (not shown).

A striker mass 39 is shown in its locked position in FIGS. 4 and 5 c.The striker mass 39 is provided with vertical recesses 40 that are usedto engage the posts 33 and serve as guides to allow the striker mass 39to ride down along the length of the posts 33 without rotation with anessentially pure up and down translational motion. In its illustratedposition in FIGS. 4 and 5 c, the striker mass 39 is locked in its axialposition to the posts 33 by at least one setback locking ball 42. Thesetback locking ball 42 locks the striker mass 39 to the posts 33 of theinertial igniter body 31 through the holes 41 provided in the posts 33and a concave portion such as a dimple (or groove) 43 on the strikermass 39 as shown in FIG. 4. A setback spring 44 with essentially deadcoil section 45, which is preferably in compression, is also providedaround but close to the posts as shown in FIGS. 4 and 5 c. In theconfiguration shown in FIG. 4, the locking balls 42 are prevented frommoving away from their aforementioned locking position by the dead coilsection 45 of the setback spring 44. The dead coil section 45 can rideup and down beyond the posts 33 as shown in FIGS. 4 and 5 c, but isbiased to stay in its upper most position as shown in the schematic ofFIG. 4 by the setback spring 44.

In this embodiment, a two-part pyrotechnics compound is shown to beused, FIG. 4. One part of the two-part pyrotechnics compound 47 (e.g.,potassium chlorate) is provided on the interior side of the base 32,preferably in a provided recess (not shown) over the exit holes 38. Thesecond part of the pyrotechnics compound (e.g., red phosphorous) 46 isprovided on the lower surface of the striker mass surface 39 facing thefirst part of the pyrotechnics compound 47 as shown in FIG. 4. Thesurfaces to which the pyrotechnic parts 46 and 47 are attached areroughened and/or provided with surface cuts, recesses, or the like ascommonly used in the art (not shown) to ensure secure attachment of thepyrotechnics materials to the applied surfaces.

In general, various combinations of pyrotechnic materials may be usedfor this purpose. One commonly used pyrotechnic material consists of redphosphorous or nano-aluminum, indicated as element 46 in FIG. 4, and isused with an appropriate binder (such as vinyl alcohol acetate resin ornitrocellulose) to firmly adhere to the bottom surface of the strikermass 39. The second component can be potassium chlorate, potassiumnitrate, or potassium perchlorate, indicated as element 47 in FIG. 4,and is used with a binder (preferably but not limited to with such asvinyl alcohol acetate resin or nitrocellulose) to firmly attach thecompound to the surface of the base 32 (preferably inside of a recessprovided in the base 32—not shown) as shown in FIG. 4.

The basic operation of the disclosed inertial igniter 30 will now bedescribed with reference to FIGS. 4-8. Any non-trivial acceleration inthe axial direction 48 which can cause dead coil section 45 to overcomethe resisting force of the setback spring 44 will initiate and sustainsome downward motion of only the dead coil section 45. The force due tothe acceleration on the striker mass 39 is supported at the dimples 43by the locking balls 42 which are constrained inside the holes 41 in theposts 33. If an acceleration time in the axial direction 48 imparts asufficient impulse to the dead coil section 45 (i.e., if an accelerationtime profile is greater than a predetermined threshold), it willtranslate down along the axis of the assembly until the setback lockingballs 42 are no longer constrained to engage the striker mass 39 to theposts 33 of the housing 31. If the acceleration event is not sufficientto provide this motion (i.e., the acceleration time profile providesless impulse than the predetermined threshold), the dead coil section 45will return to its start (top) position under the force of the setbackspring 44. The schematic of the inertial igniter 30 with the dead coilsection 45 moved down certain distance d1 as a result of an accelerationevent, which is not sufficient to unlock the striker mass 39 from theposts 33 of the housing 31, is shown in FIG. 6.

Assuming that the acceleration time profile was at or above thespecified “all-fire” profile, the dead coil section 45 will havetranslated down full-stroke d2, allowing the striker mass 39 toaccelerate down towards the base 32. In such a situation, since thelocking balls 42 are no longer constrained by the dead coil section 45,the downward force that the striker mass 39 has been exerting on thelocking balls 42 will force the locking balls 42 to move outward in theradial direction. Once the locking balls 42 are out of the way of thedimples 43, the downward motion of the striker mass 39 is impeded onlyby the elastic force of the setback spring 44, which is easily overcomeby the impulse provided to the striker mass 39. As a result, the strikermass 39 moves downward, causing the parts 46 and 47 of the two-partpyrotechnic compound to strike with the requisite energy to initiateignition. The configuration of the inertial igniter 30 when the balls 42are free to move outward in the radial direction, thereby releasing thestriker mass 39 is shown in the schematic of FIG. 7. The configurationof the inertial igniter 30 when the part 46 of the two-part pyrotechniccompound is striking the part 47 is shown in the schematic of FIG. 8.

In another embodiment, the dead coil section 45 may be constructed as aseparate collar and positioned similarly over the setback spring 44. Thecollar replacing the dead coil section 45 may also be attached to thetop coil of the setback spring 44, e.g., by welding, brazing, oradhesives such as epoxy, or the like. The advantage of attaching thecollar to the top of the setback spring 44 is that it would help preventit to get struck over the posts 33 as it is being pushed down by theapplied acceleration in the direction of the arrow 48, FIGS. 6-8.

Alternatively, the dead coil section 45 and the setback spring 44 may beintegral, made out of, for example, a cylindrical section with spiral orother type shaped cuts over its lower section to provide the requiredaxial flexibility to serve the function of the setback spring 44. Theupper portion of this cylinder is preferably left intact to serve thefunction of the dead coil section 45, FIGS. 6-8.

It is appreciated by those skilled in the art that by varying the massof the striker 39, the mass of the dead coil section 45, the spring rateof the setback spring 44, the distance that the dead coil section 45 hasto travel downward to release the locking balls 42 and thereby releasethe striker mass 39, and the distance between the parts 46 and 47 of thetwo-part pyrotechnic compound, the designer of the disclosed inertialigniter 30 can match the fire and no-fire impulse level requirements forvarious applications as well as the safety (delay or dwell action)protection against accidental dropping of the inertial igniter and/orthe munitions or the like within which it is assembled.

Briefly, the safety system parameters, i.e., the mass of the dead coilsection 45, the spring rate of the setback spring 44 and the dwellstroke (the distance that the dead coil section 44 has to traveldownward to release the locking balls 42 and thereby release the strikermass 39) must be tuned to provide the required actuation performancecharacteristics. Similarly, to provide the requisite impact energy, themass of the striker 39 and the separation distance between the parts 46and 47 of the two-part pyrotechnic compound must work together toprovide the specified impact energy to initiate the pyrotechnic compoundwhen subjected to the remaining portion of the prescribed initiationacceleration profile after the safety system has been actuated.

In addition, since the safety and striker systems each require a certainactuation distance to achieve the necessary performance, the mostaxially compact design is realized by nesting the two systems inparallel as it is done in the embodiment of FIG. 4. It is this nestingof the two safety and striker systems that allows the height of thedisclosed inertial igniter to be significantly shorter than thecurrently available inertial igniter design (as shown in FIG. 2), inwhich the safety and striker systems are configured in series. In fact,an initial prototype of the disclosed inertial igniter 30 has beendesigned to the fire and no-fire and safety specifications of thecurrently available inertial igniter shown in FIG. 2 and has achievedheight and volume reductions of over 60 percent. It is noted that byoptimizing the parameters of the disclosed inertial igniter, both heightand volume can be further reduced.

In another embodiment, the two-part pyrotechnics 46 and 47, FIG. 4, arereplaced by a percussion cap primer 49 attached to the base 32 of theinertial igniter 60 and a striker tip 50 as shown in the schematic of across-section of FIG. 9. In this illustration, all components are thesame as those shown in FIG. 4 with the exception of replacing thepercussion cap primer 49 and the striker tip 50 with striker assembly.The striker tip 50 is firmly attached to the striker mass 39.

The striker mass 39 and striker tip 50 may be a monolithic design withthe striking tip 50 being a machined boss protruding from the strikermass, or the striker tip 50 may be a separate piece pressed or otherwisepermanently fixed to the striker mass. A two-piece design would befavorable to the need for a striker whose density is different thansteel, but whose tip would remain hard and tough by attaching a steelball, hemisphere, or other shape to the striker mass. A monolithicdesign, however, would be generally favorable to manufacturing becauseof the reduction of part quantity and assembly operations.

An advantage of using the two component pyrotechnic materials as shownin FIG. 4 is that these materials can be selected such that ignition isprovided at significantly lower impact forces than are required forcommonly used percussion cap primers. As a result, the amount ofdistance that the striker mass 39 has to travel and its required mass isthereby reduced, resulting in a smaller total height (shown as 15 inFIG. 1) of the thermal battery assembly. This choice, however, has thedisadvantage of not using standard and off-the-shelf percussion capprimers, thereby increasing the component and assembly cost of theinertial igniter.

The disclosed inertial igniters are seen to discharge the ignition fireand sparks directly into the thermal battery, FIGS. 4-9, to ignite thepyrotechnic materials 24 within the thermal battery 11 (FIG. 3). As aresult, the additional housing 21 and ignition material 23 shown in FIG.3 can be eliminated, greatly simplifying the resulting thermal batterydesign and manufacture. In addition, the total height 13 and volume ofthe inertial igniter assembly 10 and the total height 15 of the completethermal battery assembly 16 are reduced, thereby reducing the totalvolume that has to be allocated in munitions or the like to house thethermal battery.

The disclosed inertial igniters are shown sealed within their housing,thereby simplifying their storage and increase their shelf life.

FIG. 10 shows the schematic of a cross-section of another embodiment 80.This embodiment is similar to the embodiment shown in FIGS. 4-8, withthe difference that the striker mass 39 (FIGS. 4-8) is replaced with astriker mass 82, with at least one opening passage 81 to guide theignition flame up through the igniter 80 to allow the pyrotechnicmaterials (or the like) of a thermal battery (or the like) positionedabove the igniter 80 (not shown) to be initiated. In addition, the topcap 35 (FIG. 4-8) is preferably eliminated or replaced by a cap 83 withappropriately positioned openings to allow the flames to enter thethermal battery and initiate its pyrotechnic materials. The openings 38(FIG. 5 b) are obviously no longer necessary.

FIG. 11 b shows the schematic of a cross-section of another embodiment90. This embodiment is similar to the embodiment shown in FIGS. 4-8,with the difference that the openings 38 (FIG. 5 b) for the flame toexit the igniter 30 is replaced with side openings 91, FIG. 11 a, toallow the flame to exit from the side of the igniter to initiate thepyrotechnic materials (or the like) of a thermal battery or the like(not shown) that is positioned around the body of the igniter 90.Alternatively, the igniter housing 92 may be eliminated, therebyallowing the generated ignition flames to directly flow to the sides ofthe igniter 90 and initiate the pyrotechnic materials of the thermalbattery or the like.

FIG. 12 shows the schematic of a cross-section of another embodiment100. This embodiment is similar to the embodiment shown in FIGS. 4-8,with the difference that the dead coil section 45 (FIGS. 4-5) isreplaced with a solid, preferably relatively very rigid, cylindricalsection 101. The advantage of using a rigid cylindrical section 101 isthat the balls 42 (FIGS. 4-5) would not tend to cause the individualcoils of the dead coil section 45 to move away from their cylindricallypositioned configuration, thereby increasing the probability that thedead coil section could get stuck by the friction forces due to thepressure exerted by the balls 42 to the interior of the housing 34 (FIG.4) or other similar possible scenarios.

In certain applications, the required reliability levels for initiationof inertial igniters are extremely high. In certain cases, the ignitersshould be designed and manufactured to perform their function withextremely high reliability of nearly 100 percent. Some cases may evenrequire the use of multiple and redundant inertial igniters to obtainnearly 100 percent reliability.

The cost issue is also another important consideration since in smallthermal batteries that have to be initiated by inertial igniters, thecost of inertial igniters may easily be a significant portion of thetotal cost. However, to significantly reduce the cost, inertial ignitershave to be designed with fewer and easy to manufacture parts and be easyto assemble. In addition, the inertial igniters must use mass producedand commercially available parts.

The embodiments of the inertial igniters disclosed below are to providethe aforementioned advantages of the embodiments shown in FIGS. 4-12 andin addition: (1) provide inertial igniters that are significantly morereliable and easy to manufacture than currently available inertialigniters for thermal batteries or the like, particularly for relativelysmall thermal batteries that are used in munitions; (2) provide highlyreliable and at the same time very small inertial igniters that do notoccupy a significant volumes of small thermal batteries; (3) provideinertial igniters that are easy to manufacture and assemble into thermalbatteries; and (4) provide inertial igniters that are readily modifiedto satisfy a wide range of no-fire and all-fire requirements withoutrequiring costly engineering development and manufacturing equipmentchanges.

A need exists for novel miniature inertial igniters for thermalbatteries used in gun fired munitions, that are extremely reliable, lowcost (such as having fewer easy to manufacture parts that are notrequired to be fabricated to very low tolerances), easy to manufactureand assemble, and easy to assemble into a thermal battery (such assimply “drop-in” component during thermal battery assembly). Suchinertial igniters can also be adaptable to a wide range of all-fire andno-fire requirements without requiring a significant amount ofengineering development and testing. Such inertial igniters can also becapable of allowing multiple inertial igniters to be readily packed intothermal batteries as redundant initiators to further increase initiationreliability when such extremely high initiation reliability arewarranted. Such inertial igniters are particularly needed for small andlow power thermal batteries that could be used in fuzing and othersimilar applications. Such inertial igniters must be safe and in generaland in particular they should not initiate if dropped, e.g., from up to5-7 feet onto a concrete floor for certain applications; shouldwithstand high firing accelerations and do not cause damage to thethermal battery, for example up to 20-50,000 Gs or even more; and shouldbe able to be designed to ignite at specified acceleration levels whensubjected to such accelerations for a specified amount of time to matchthe firing acceleration experienced in a gun barrel as compared to highG accelerations experienced during accidental falls which last for veryshort periods of time, for example accelerations of the order of 1000 Gswhen applied for over 5 msec as experienced in a gun as compared to, forexample 2000 G acceleration levels experienced during accidental fallover a concrete floor but which may last only 0.5 msec. Reliability isalso of much concern since the rounds should have a shelf life of up to20 years and could generally be stored at temperatures of sometimes inthe range of −65 to 165 degrees F. This requirement is usually satisfiedbest if the igniter pyrotechnic is in a sealed compartment.

An isometric cross-sectional view of a sixth embodiment of an inertiaigniter is shown in FIG. 13, referred to generally with referencenumeral 200. The full isometric view of the inertial igniter 200 isshown in FIG. 14. The inertial igniter 200 is constructed with igniterbody 201, consisting of a base 202 and at least three posts 203. Thebase 202 and the at least three posts 203, can be integrally formed as asingle piece but may also be constructed as separate pieces and joinedtogether, for example by welding or press fitting or other methodscommonly used in the art. The base 202 of the housing can also beprovided with at least one opening 204 (with a corresponding opening(s)in the thermal battery—not shown) to allow ignited sparks and fire toexit the inertial igniter and enter into the thermal battery positionedunder the inertial igniter 200 upon initiation of the inertial igniterpyrotechnics 215, or percussion cap primer when used in place of thepyrotechnics, similar to the primer 49 in the embodiment 60 shown inFIG. 9. Although illustrated with the opening 204 in the base, theopening (or openings) can alternatively be formed in a side wall as isshown in FIG. 11 a or in the striker mass as is shown in FIG. 10.

The base 202 of the housing may be extended to form a cap for thethermal battery, similar to the cap 36 of the thermal battery 37 shownfor the embodiment 30 in FIGS. 4 and 5.

A striker mass 205 is shown in its locked position in FIG. 13. Thestriker mass 205 is provided with guides for the posts 203, such asvertical surfaces 206 (which may be recessed as shown in the embodiment30 in FIGS. 4 and 5), that are used to engage the corresponding (inner)surfaces of the posts 203 and serve as guides to allow the striker mass205 to ride down along the length of the posts 203 without rotation withan essentially pure up and down translational motion. However, thesurfaces 206 minimize the chances of the striker mass 205 jamming ascompared to the recesses 40. Further, manufacturing precision is reduced(for both the posts 203 and the striker mass 205) when the surfaces 206are used in place of the recesses 40. Consequently, both the strikermass 205 and the inertial igniter structure (which includes the posts203) is easier to produce and less costly when the surfaces 206 are usedin place of the recesses 40.

In its illustrated position in FIGS. 13 and 14, the striker mass 205 islocked in its axial position to the posts 203 by at least one setbacklocking ball 207. The setback locking ball 207 locks the striker mass205 to the posts 203 of the inertial igniter body 201 through the holes208 provided in the posts 203 and a concave portion such as a dimple (orgroove) 209 on the striker mass 205 as shown in FIG. 13. A setbackspring 210, which is preferably in compression, is also provided aroundbut close to the posts 203 as shown in FIGS. 13 and 14. In theconfiguration shown in FIG. 13, the locking balls 207 are prevented frommoving away from their aforementioned locking position by the collar211. The setback spring 210 can be a wave spring with rectangularcross-section. The rectangular cross-section eliminates the need to fixor otherwise retain the striker spring 210 to the collar 211, which isan expensive process; the flat coil spring surfaces minimizes thechances of coils slipping laterally (perpendicular to the direction ofacceleration 218), which can cause jamming and prevent the release ofthe striker mass 205 (preventing the collar to move down enough torelease the locking balls). Furthermore, wave springs generate frictionbetween the waves at contact points along the spring wire, therebyreducing the chances for the collar 211 to rapidly bounce back up andpreventing the striker mass 205 from being released.

The collar 211 is preferably provided with partial guide 212 (“pocket”),which are open on the top as indicated by the numeral 213. The guide 212may be provided only at the location of the locking balls 207 as shownin FIGS. 13 and 14, or may be provided as an internal surface over theentire inner surface of the collar 211 (not shown). The advantage ofproviding local guides 212 is that it results in a significantly largersurface contact between the collar 211 and the outer surfaces of theposts 203, thereby allowing for smoother movement of the collar 211 upand down along the length of the posts 203. In addition, they preventthe collar 211 from rotating relative to the inertial igniter body 201and makes the collar stronger and more massive. The advantage ofproviding a continuous inner recess guiding surface for the lockingballs 207 is that it would require fewer machining processes during thecollar manufacture. Although only one locking ball 207 is illustrated inFIG. 13, more than one can be provided, such as a locking ball 207associated with each post 203. More than one locking ball 207 can alsobe associated with each post 203.

The collar 211 rides up and down on the posts 203 as can be seen inFIGS. 13 and 14, but is biased to stay in its upper most position asshown in FIGS. 13 and 14 by the setback spring 210. The guides 212 areprovided with bottom ends 214, so that when the inertial igniter isassembled as shown in FIGS. 13 and 14, the setback spring 210 which isbiased (preloaded) to push the collar 211 upward away from the igniterbase 201, would “lock” the collar 211 in its uppermost position againstthe locking balls 207. As a result, the assembled inertial igniter 200stays in its assembled state and would not require a top can (similar tothe top cap 35 in the embodiment 30 of FIG. 4) to prevent the collar 211from being pushed up and allowing the locking balls 207 from moving outand releasing the striker mass 205.

In the sixth embodiment, a one part pyrotechnics compound 215 (such aslead styphnate or other similar compound) can be used as shown in FIG.13. The surfaces to which the pyrotechnic compound 215 is attached canbe roughened and/or provided with surface cuts, recesses, projections,or the like and/or treated chemically as commonly done in the art (notshown) to ensure secure attachment of the pyrotechnics material to theapplied surfaces. The use of one part pyrotechnics compound makes themanufacturing and assembly process much simpler and thereby leads tolower inertial igniter cost. The striker mass can be provided with arelatively sharp tip 216 and the igniter base surface 202 is providedwith a protruding tip 217 which is covered with the pyrotechnicscompound 215, such that as the striker mass is released during anall-fire event and is accelerated down (opposite to the arrow 218illustrated in FIG. 13), impact occurs mostly between the surfaces ofthe tips 216 and 217, thereby pinching the pyrotechnics compound 215,thereby providing the means to obtain a reliable initiation of thepyrotechnics compound 215.

Alternatively, a two-part pyrotechnics compound as shown and describedfor the embodiment 30 of FIG. 4 can be used. One part of the two-partpyrotechnics compound 47 (FIG. 4), e.g., potassium chlorate, can beprovided on the interior side of the base 32, such as in a providedrecess (not shown) over the exit holes 38. The second part of thepyrotechnics compound (e.g., red phosphorous) 46 can be provided on thelower surface of the striker mass surface 39 facing the first part ofthe pyrotechnics compound 47, as shown in FIG. 4. In general, variouscombinations of pyrotechnic materials can be used for this purpose. Onecommonly used pyrotechnic material consists of red phosphorous ornano-aluminum, indicated as element 46 in FIG. 4, and is used with anappropriate binder (such as vinyl alcohol acetate resin ornitrocellulose) to firmly adhere to the bottom surface of the strikermass 39. The second component can be potassium chlorate, potassiumnitrate, or potassium perchlorate, indicated as element 47 in FIG. 4,and is used with a binder (such as, but not limited to vinyl alcoholacetate resin or nitrocellulose) to firmly attach the compound to thesurface of the base 32 (such as inside of a recess provided in the base32—not shown) as shown in FIG. 4.

Alternatively, instead of using the pyrotechnics compound 215, FIG. 13,a percussion cap primer or the like (similar to the percussion capprimer 49 used in the embodiment 60 of FIG. 9) can be used. A strikertip (similar to the striker tip 50 shown in FIG. 9 for the embodiment60) can be provided at the tip 216 of the striker mass 205 (not shown)to facilitate initiation upon impact.

The basic operation of the embodiment 200 of the inertial igniter ofFIGS. 13 and 14 is similar to that of embodiment 30 (FIGS. 4-8) aspreviously described. Here again, any non-trivial acceleration in theaxial direction 218 which can cause the collar 211 to overcome theresisting force of the setback spring 210 will initiate and sustain somedownward motion of the collar 211. The force due to the acceleration onthe striker mass 205 is supported at the dimples 209 by the lockingballs 207 which are constrained inside the holes 208 in the posts 203.If an acceleration time in the axial direction 218 imparts a sufficientimpulse to the collar 211 (i.e., if an acceleration time profile isgreater than a predetermined threshold), it will translate down alongthe axis of the assembly until the setback locking balls 205 are nolonger constrained to engage the striker mass 205 to the posts 203. Ifthe acceleration event is not sufficient to provide this motion (i.e.,the acceleration time profile provides less impulse than thepredetermined threshold), the collar 211 will return to its start (top)position under the force of the setback spring 210.

Assuming that the acceleration time profile was at or above thespecified “all-fire” profile, the collar 211 will have translated downpast the locking balls 207, allowing the striker mass 205 to acceleratedown towards the base 202. In such a situation, since the locking balls207 are no longer constrained by the collar 211, the downward force thatthe striker mass 205 has been exerting on the locking balls 207 willforce the locking balls 207 to move outward in the radial direction.Once the locking balls 207 are out of the way of the dimples 209, thedownward motion of the striker mass 205 is impeded only by the elasticforce of the setback spring 210, which is easily overcome by the impulseprovided to the striker mass 205. As a result, the striker mass 205moves downward, causing the tip 216 of the striker mass 205 to strikethe pyrotechnic compound 215 on the surface of the protrusion 217 withthe requisite energy to initiate ignition (similar to the configurationshown for the embodiment 30 in FIG. 8).

In the embodiment 200 of the inertial igniter shown in FIGS. 13 and 14,the setback spring 210 is illustrated as a helical wave spring typefabricated with rectangular cross-sectional wires (such as the onesmanufactured by Smalley Steel Ring Company of Lake Zurich, Ill.). Thisis in contrast with the helical springs with circular wirecross-sections used in the embodiments of FIGS. 4-12. The use of theaforementioned rectangular cross-section wave springs or the like hasthe following significant advantages over helical springs that areconstructed with wires with circular cross-sections. Firstly and mostimportantly, as the spring is compressed and nears its “solid” length,the flat surfaces of the rectangular cross-section wires come in contactand generate minimal lateral forces that would otherwise tend to forceone coil to move laterally relative to the other coils as is usually thecase when the wires are circular in cross-section. Lateral movement ofthe coils can, in general, interfere with the proper operation of theinertial igniter since it could, for example jam a coil to the outerhousing of the inertial igniter (not shown in FIGS. 13 and 14), which isusually desired to house the igniter 200 or the like with minimalclearance to minimize the total volume of the inertial igniter. Inaddition, the laterally moving coils could also jam against the posts203 thereby further interfering with the proper operation of theinertial igniter. The use of the present wave springs with rectangularcross-section eliminates such lateral movement and thereforesignificantly increases the reliability of the inertial igniter and alsosignificantly increases the repeatability of the initiation for aspecified all-fire condition. The second advantage of the use of theaforementioned wave springs with rectangular cross-section, particularlysince the wires can and are usually made thin in thickness andrelatively wide, the solid length of the resulting wave spring can bemade to be significantly less than an equivalent regular helical springwith circular cross-section. As a result, the total height of theresulting inertial igniter can be reduced. Thirdly, since the coil wavesare in contact with each other at certain points along their lengths andas the spring is compressed, the length of each wave is slightlyincreased, therefore during the spring compression the friction forcesat these contact points do a certain amount of work and thereby absorb acertain amount of energy. The presence of such friction forces ensuresthat the firing acceleration and very rapid compression of the springwould to a lesser amount tend to “bounce” the collar 211 back up andthereby increasing the possibility that it would interfere with the exitof the locking balls from the dimples 209 of the striker mass 205 andthe release of the striker mass 205. The above characteristic of thewave springs with rectangular cross-section therefore also significantlyenhances the performance and reliability of the inertial igniter 200while at the same time allowing its height (and total volume) to bereduced.

It is appreciated by those skilled in the art that by varying the massof the striker 205, the mass of the collar 211, the spring rate of thesetback spring 210, the distance that the collar 211 has to traveldownward to release the locking balls 207 and thereby release thestriker mass 205, and the distance between the tip 216 of the strikermass 205 and the pyrotechnic compound 215 (and the tip of the protrusion217), the designer of the disclosed inertial igniter 200 can match theall-fire and no-fire impulse level requirements for various applicationsas well as the safety (delay or dwell action) protection againstaccidental dropping of the inertial igniter and/or the munitions or thelike within which it is assembled.

Briefly, the safety system parameters, i.e., the mass of the collar 211,the spring rate of the setback spring 210 and the dwell stroke (thedistance that the collar 210 has to travel downward to release thelocking balls 207 and thereby release the striker mass 205) must betuned to provide the required actuation performance characteristics.Similarly, to provide the requisite impact energy, the mass of thestriker 205 and the aforementioned separation distance between the tip216 of the striker mass and the pyrotechnic compound 215 (and the tip ofthe protrusion 217) must work together to provide the specified impactenergy to initiate the pyrotechnic compound when subjected to theremaining portion of the prescribed initiation acceleration profileafter the safety system has been actuated.

The striker mass 205 and striker tip 216 may be a monolithic design withthe striking tip 216 being formed, as shown in FIG. 13, or as a bossprotruding from the striker mass, or the striker tip 216 may be aseparate piece, possibly fabricated from a material that issignificantly harder than the striker mass material, and pressed orotherwise permanently fixed to the striker mass. A two-piece designwould be favorable to the need for a striker whose density is differentthan steel, but whose tip would remain hard and tough by attaching asteel ball, hemisphere, or other shape to the striker mass. A monolithicdesign, however, would be generally favorable to manufacturing becauseof the reduction of part quantity and assembly operations.

The use of three or more posts 203 in the embodiment 200 of FIGS. 13 and14 has several significant advantages over the two post designs of theembodiments of FIGS. 4-5. namely, unlike the embodiment 30 of FIGS. 4and 5 in which the striker mass 39 is provided with vertical recesses 40that are used to engage the posts 33 and serve as guides to allow thestriker mass 39 to ride down along the length of the posts 33 withoutrotation, the use of at least three posts 203 in the embodiment 200 ofFIGS. 13 and 14 eliminates the need for the aforementioned verticalrecesses in the striker mass 205. As a result, the chances that thestriker mass 203 gets jammed at the interface between the aforementionedvertical recesses (40 in FIGS. 4 and 5) and the posts (33 in FIGS. 4 and5) are almost entirely eliminated. As a result, the reliability of theinertial igniter is significantly increased. Furthermore, the design ofthe striker mass and the igniter posts and their required manufacturingprocess are significantly simplified and the required manufacturingprecision is also reduced. As a result, the manufacturing cost of thestriker mass as well as the igniter body is significantly reduced. Stillfurther, the contacting surfaces between the striker mass 205 and theposts 203 is increased, thereby allowing for a smoother up and downmovement of the striker mass 205 along the inner surfaces of the posts203.

In the embodiment 200 of FIGS. 13 and 14, following ignition of thepyrotechnics compound 215, the generated flames and sparks are designedto exit downward through the opening 204 to initiate the thermal batterybelow. Alternatively, if the thermal battery is positioned above theinertial igniter 200, the opening 204 can be eliminated and the strikermass could be provided with at least one opening similar to the passage81 of the striker mass 82 of the embodiment 80 of FIG. 10 to guide theignition flame and sparks up through the striker mass 205 to allow thepyrotechnic materials (or the like) of a thermal battery (or the like)positioned above the inertial igniter 200 (not shown) to be initiated.

Alternatively, in a manner similar to that shown in the embodiment 90 ofFIGS. 11 a and 11 b, side ports (openings 91) may be provided to allowthe flame to exit from the side of the igniter to initiate thepyrotechnic materials (or the like) of a thermal battery or the likethat is positioned around the body of the inertial igniter.Alternatively, the igniter housing 261 (FIG. 16) may be eliminated,thereby allowing the generated ignition flames to directly flow to thesides of the igniter 200 and initiate the pyrotechnic materials of thethermal battery or the like.

In FIGS. 13 and 14, the inertial igniter embodiment 200 is shown withoutany outside housing. In many applications, as shown in the schematics ofFIG. 15 a (15 b), the inertial igniter 240 (250) is placed securelyinside the thermal battery 241 (251), either on the top (FIG. 15 a) orbottom (FIG. 15 b) of the thermal battery housing 242 (252). This isparticularly the case for relatively small thermal batteries. In suchthermal battery configurations, since the inertial igniter 240 (250) isinside the hermetically sealed thermal battery 241 (251), there is noneed for a separate housing to be provided for the inertial igniteritself. In this assembly configuration, the thermal battery housing 242(252) is provided with a separate compartment 243 (253) for the inertialigniter. The inertial igniter compartment 243 (253) is preferably formedby a member 244 (254) which is fixed to the inner surface of the thermalbattery housing 242 (253), preferably by welding, brazing or very strongadhesives or the like. The separating member 244 (254) is provided withan opening 245 (255) to allow the generated flame and sparks followingthe initiation of the inertial igniter 240 (250) to enter the thermalbattery compartment 246 (256) to activate the thermal battery 241 (251).The separating member 244 (254) and its attachment to the internalsurface of the thermal battery housing 242 (252) must be strong enoughto withstand the forces generated by the firing acceleration.

For larger thermal batteries, a separate compartment (similar to thecompartment 10 over or possibly under the thermal battery hosing 11 asshown in FIG. 1 can be provided above, inside or under the thermalbattery housing for the inertial igniter. An appropriate opening(similar to the opening 12 in FIG. 1) can also be provided to allow theflame and sparks generated as a result of inertial igniter initiation toenter the thermal battery compartment (similar to the compartment 14 inFIG. 1) and activate the thermal battery.

The inertial igniter 200, FIGS. 13 and 14 may also be provided with ahousing 260 as shown in FIG. 16. The housing 260 is preferably one pieceand fixed to the base 202 of the inertial igniter structure 201,preferably by soldering, laser welding or appropriate epoxy adhesive orany other of the commonly used techniques to achieve a sealedcompartment. The housing 260 may also be crimped to the base 202 asshown in FIG. 16 for the inertial igniter embodiment 30. The housing 260may also be crimped to the base 202 at its open end 261, in which casethe base 202 is preferably provided with an appropriate recess 262 toreceive the crimped portion 261 of the housing 260. The housing can besealed at or near the crimped region via one of the commonly usedtechniques such as those described above.

In addition, as shown in FIG. 17, the base 202 of the inertial igniter200 may be extended to form the cap 263, which could be used to form thetop cap of the thermal battery as is shown in FIG. 5 c and identifiedwith the numeral 36 for the inertial igniter embodiment 30.

The inertial igniter embodiment 200 of FIGS. 13 and 14 as provided withthe aforementioned housing 260 and shown in FIG. 16 may also behermetically sealed. To this end, and as shown in FIG. 18, the opening204 can be covered, preferably with a thin membrane 264. The membrane264 can be an integral part of the base 202 and is scorched on itsbottom surface (not seen in the view of FIG. 18) to assist it to breakopen by the pressure generated by the initiation of the pyrotechnicscompound 215 (FIG. 13) upon initiation of the inertial igniter to allowthe generated flame and sparks to enter the thermal battery through theresulting opening.

In another embodiment, more than one inertial igniter, preferablyinertial igniters of the embodiment 200 type are used in a thermalbattery to significantly increase the overall reliability of the thermalbattery initiation under all-fire condition. As a result, if for anyreason one of the inertial igniters fails to initiate or fails toinitiate the thermal battery, then there would be one or more(redundant) inertial igniters to significantly reduce the chances thatthe thermal battery would fail to be activated. The more than oneinertial igniters (preferably of embodiment 200 or any other of theaforementioned embodiments) may in general be assembled in anyappropriate configuration in the thermal battery. For the case of smallthermal batteries, however and if the thermal battery size allows, theinertial igniters are preferably ganged up together in one location, forexample on the top or bottom compartments shown in FIGS. 15 a and 15 bor in the compartment 10 shown in FIG. 1, to minimize the total volumeand size occupied by the inertial igniters. For example, when threeinertial igniters of the embodiment 200 are to be assembled within athermal battery, for example of the type shown in FIG. 15 a, assumingthat the amount of space available in the compartment 243 isappropriate, the three inertial igniters 200 may be ganged up inside thecompartment 243 as shown in the top view of FIG. 19 (the top cap isremoved to show the inertial igniters 200 inside the compartment 243).

When more than one inertial igniter 200 (or of other embodiment types)are ganged up in a compartment similar to that of 243 as shown in FIG.19, the body 201 of two or more of the inertial igniters 200 may beintegral. For example, the bodies 201 of the three inertial igniters 200shown in FIG. 19 may be integral as shown in the top and isometric viewsof FIGS. 20 a and 20 b, respectively, and identified with referencenumeral 265.

In certain applications, it is desired that the inertial igniters gangedup in a compartment such as 243 as shown in FIG. 19 be separated by awall so that their operations and/or failure (such as flying piecesfollowing initiation or break up of one igniter) would not interferewith the operation of the remaining inertial igniters. In such cases,the inertial igniter bodies (such as the bodies 201 of the inertialigniters 200, FIGS. 13 and 19) and the separation walls 206 between atleast two of the inertial igniters may be integral as shown in theisometric and top views of FIGS. 21 a and 21 b, respectively, andindicated by reference numeral 266. In the drawings of FIGS. 21 a and 21b, all three inertial igniters 200 are intended to be separated fromeach other by the walls 267.

The present inertial igniters are designed such that when ganged up asshown in FIG. 20 a or FIG. 21 a, their integral bodies 201 can bereadily machined, for example from a solid rod, using commonly used CNCmachining centers or the like.

While there has been shown and described what is considered to bepreferred embodiments of the invention, it will, of course, beunderstood that various modifications and changes in form or detailcould readily be made without departing from the spirit of theinvention. It is therefore intended that the invention be not limited tothe exact forms described and illustrated, but should be constructed tocover all modifications that may fall within the scope of the appendedclaims.

1. An inertial igniter comprising: a body having a base and three ormore posts extending from the base, each of the three or more postshaving a hole; at least one locking ball corresponding to each of thethree of more posts, wherein a first portion of the locking balls aredisposed in the hole; a striker mass movably disposed relative to thethree or more posts and having a surface corresponding to each of thethree or more posts, the movement of the striker mass being guided bythe surfaces, the striker mass further having a concave portioncorresponding to each of the locking balls, wherein a second portion ofeach locking ball is disposed in a corresponding concave portion forretaining the striker mass relative to the three or more posts; a collarmovable relative to the three or more posts; and a biasing element forbiasing the collar in a first position which retains the locking ballswithin the concave portions, the biasing element permitting movement ofthe collar to a second position in which the locking balls can bereleased from the concave portions to release the striker mass relativeto the three or more posts upon a predetermined acceleration profileexperienced by the body.
 2. The inertial igniter of claim 1, wherein thesurfaces are planar.
 3. The inertial igniter of claim 1, wherein thebiasing element is a compression spring disposed between a portion ofthe base and a portion of the collar.
 4. The inertial igniter of claim3, wherein the compression spring is a wave spring having a rectangularcross-section.
 5. The inertial igniter of claim 3, wherein the collarfurther comprises a guide having a bottom and an opening at a top,wherein the bottom and top are oriented in a direction of acceleration,a third portion of the locking balls being seated at the bottom.
 6. Theinertial igniter of claim 5, wherein the guide is formed around acontinuous surface of the collar.
 7. The inertial igniter of claim 5,wherein the guide comprises three or more guides, each corresponding toeach of the three or more locking balls.
 8. The inertial igniter ofclaim 1, further comprising one or more pyrotechnic materials disposedon the base for creating a spark upon contact of the striker mass withthe base.
 9. The inertial igniter of claim 8, wherein the base furtherincludes at least one opening for allowing the spark to pass into athermal battery attached to the base.
 10. The inertial igniter of claim8, wherein the striker mass further includes a first projection forfacilitating ignition of the one or more pyrotechnic materials when thestriker mass contacts the base.
 11. The inertial igniter of claim 9,wherein the base further includes a second projection corresponding tothe first projection and covered by the one or more pyrotechnicmaterials, the second projection being aligned with the first projectionsuch that the first and second projections contact first when thestriker mass contacts the base.
 12. The inertial igniter of claim 8,wherein the one or more pyrotechnic materials is a one-part pyrotechnicmaterial formed on the base.
 13. The inertial igniter of claim 12,wherein the one-part pyrotechnic material is lead styphnate.
 14. Theinertial igniter of claim 1, further comprising percussion cap primerdisposed on the base for creating a spark upon contact of the strikermass with the base.
 15. The inertial igniter of claim 1, wherein thebase and three or more posts are integrally formed.
 16. The inertialIgniter of claim 1, further comprising a housing connected to the basefor sealing the inertial igniter.
 17. The inertial igniter of claim 16,wherein the housing is crimped to the base.
 18. The inertial igniter ofclaim 16, wherein the base further includes at least one opening and amembrane disposed over the at least one opening, wherein the membraneopens after ignition of a pyrotechnic material formed on the base toallow a generated spark to pass into a thermal battery attached to thebase.
 19. The inertial igniter of claim 1, wherein the base extendsradially from the three or more posts to form a top cap for a thermalbattery attached to the body.
 20. The inertial igniter of claim 1,wherein the base further includes at least one opening for allowing aspark generated from contact of the striker mass with at least a portionof the base to pass into a thermal battery attached to the base.
 21. Theinertial igniter of claim 20, wherein the hole comprises one of one ormore holes disposed in the base, one or more opening on a side of thebody and one or more holes formed through the striker to allow the sparkto exit from the top of the igniter.
 22. A thermal battery comprising: ahousing having a first compartment and a second compartment; a thermalbattery housed in the first compartment; and an inertial igniter housedin the second compartment; wherein the first and second compartments areseparated by a rigid member.
 23. The thermal battery of claim 22,wherein the second compartment is oriented on top of the firstcompartment in the direction of an acceleration.
 24. The thermal batteryof claim 22, wherein the first compartment is oriented on top of thesecond compartment in the direction of an acceleration.
 25. An ignitionsystem for a thermal battery, the ignition system comprising: a baseplate for connection to the thermal battery; and two or more inertialigniters formed on the base plate, each of the two or more inertialigniters having a striker mass which ignites one or more pyrotechnicmaterials upon a predetermined acceleration profile, the base platehaving an opening corresponding to each of the two or more inertialigniters for allowing a generated spark to pass into the thermalbattery.
 26. The ignition system of claim 25, wherein the two or moreinertial igniters comprise three inertial igniters.
 27. The ignitionsystem of claim 25, wherein each of the inertial igniters comprises twoor more posts connected to the base plate for guiding the striker masstowards the one or more pyrotechnic materials, each of the two or moreposts further having a hole for housing a ball, the balls retaining thestriker mass from striking the one or more pyrotechnic materials unlessthe predetermined acceleration profile is experienced by the base plate.28. The ignition system of claim 27, wherein each of the two or moreposts are integrally formed with the base.
 29. The ignition system ofclaim 25, further comprising one or more partition walls connected tothe base for separating the base into two or more compartments, each ofthe two or more inertial igniters being disposed in one of the two ormore compartments.
 30. The ignition system of claim 29, wherein the oneor more partition walls are integrally formed with the base.